The project is to investigate the physico-chemical basis of cell fusion phenomena in model membrane as well as biological membrane systems. The project consists of a) Studies of membrane fusion between two spherical phospholipid membranes induced both thermally and chemically; b) A study of fusion between phospholipid bilayer and vesicle membranes induced by divalent ions; c) Expansion and fluidity of membrane in correlation with membrane fusion; and d) Investigation of aggregation and fusion of platelets and erythrocytes with a similar approach taken in the model membrane fusion studies. Mechanism of membrane fusion is studied in terms of membrane instability, fluidity and hydrophobic interactions. Model membranes are comprised of natural and synthetic phospholipids and membrane proteins. The platelets and erythrocytes are extracted from animal bloods. The properties measured are electrical conductance across model membranes during fusion of vesicle membranes, microscopic observation and electron-microscopy for the membrane fusion, the spectroscopic measurements of membrane aggregation, and monolayer properties (expansion, surface tension and viscosity) aggregation, to correlate membrane fusion mechanism to the membrane hydrophobicity and fluidity.